Process for producing graft copolymer

ABSTRACT

A graft copolymer produced by polymerizing an ethylenically unsaturated monomer in the presence of a fluorine-containing resin having reactive double bonds via a urethane linkage is excellent in transparency and pigment dispersibility and can provide a coating composition excellent in weather resistance.

BACKGROUND OF THE INVENTION

This invention relates to a process for producing a graft copolymer byreacting an ethylenically unsaturated monomer with a fluorine-containingresin.

Recently, from the viewpoint of saving resources and saving energy,there have strongly been desired coating compositions excellent inweather resistance, that is, providing maintenance-free coating filmeven in paint industry. Heretofore, acrylic resins have been used infields wherein weather resistance is required, but a further improvementis required now.

Further, the acrylic resins have defects in that they are generally poorin drape with pigments having higher oil absorbing properties,particularly they are remarkably poor in pigment dispersion as to carbonblack and the like pigments, they require a longer time to obtainuniform dispersion, they cause pigment separation during storage, andthe like. In order to improve the pigment dispersibility, it is proposedto synthesize an acrylic resin in the presense of an alkyd resin havingunsaturated carbon-carbon double bonds. The resulting resin is improvedin the pigment dispersibility but inferior in weather resistance andchemical resistance to the acrylic resins before modified.

On the other hand, there are known fluorine-containing copolymers havingas essential components fluoroolefin, hydroxyalkyl vinyl ether, alkylvinyl ether and cyclohexyl vinyl ether. These fluorine-containingcopolymers are excellent in weather resistance, but poor in pigmentdispersibility and initial gloss. In order to improve such defects, itis proposed to produce a graft copolymer by polymerizing anethylenically unsaturated monomer in the presence of afluorine-containing copolymer mentioned above to which reactivecarbon-carbon double bonds were introduced (Japanese Patent UnexaminedPublication No. 59-41315). The resulting graft copolymer is excellent inthe weather resistance, pigment dispersibility and initial gloss, buthas defects in that it is insufficient in compatibility with theethylenically unsaturated monomer and its polymer, the graft copolymersolution is often clouded, the pigment can disperse but is easilyseparated from the resin component, and the like.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a process for producing agraft copolymer excellent in weather resistance as well as transparencyand pigment dispersibility.

This invention provides a process for producing a graft copolymer whichcomprises polymerizing 99.5 to 0.5% by weight of an ethylenicallyunsaturated monomer (B) copolymerizable with double bonds of thefollowing resin (A) in the presence of 0.5 to 99.5% by weight of afluorine-containing resin(A) having reactive double bonds via a urethanelinkage in an amount of 0.001 to 0.025 mole per 100 g of the resin (A).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fluorine-containing resin, the component (A), should have reactivedouble bonds in an amount of 0.001 to 0.025 mole, preferably 0.002 to0.015 mole, per 100 g of the resin (A). When the amount is less than0.001 mole, the graft polymerization becomes difficult when polymerizedtogether with the component (B). On the other hand, when the amount ismore than 0.025 mole, gelation easily takes place during thepolymerization. The double bonds should be bonded via a urethanelinkage. By taking such a structure, the graft copolymer obtained isexcellent in the transparency and pigment dispersibility.

As the component (A), it is preferable to use a fluorine-containingresin having a weight average molecular weight of about 1000 to 200,000,more preferably about 10,000 to 100,000. When the molecular weight istoo low, there is a tendency to lower the weather resistance andchemical resistance. On the other hand, when the molecular weight is toohigh, there is a tendency to easily bring about gelation at the time ofreacting the component (A) with a isocyanate group-containingpolymerizable adduct, or at the time of polymerizing the component (B).

The fluorine-containing resin, the component (A), can be produced byreacting a fluorine-containing copolymer having hydroxyl groupsmentioned below with a polyvalent isocyanate compound having two or moreisocyanate groups, and an ethylenically unsaturated monomer having oneor more hydroxyl groups. In this process, it is preferable to react thepolyvalent isocyanate compound with the hydroxyl group-containingethylenically unsaturated monomer to prepare an isocyanategroup-containing polymerizable adduct, which is then reacted with thefluorine-containing copolymer having hydroxyl groups.

As the polyvalent isocyanate, there can be used compounds having two ormore isocyanate groups such as hexamethylene diisocyanate, tolylenediisocyanate, xylylene diisocyanate, isophorone diisocyanate, lysinediisocyanate, diphenylmethane diisocyanate, 2,2,4-trimethylhexamethylenediisocyanate, cyclohexylmethane diisocyanate, methylcyclohexanediisocyanate, isopropylidene bis(4-cyclohexylisocyanate), hexamethylenediisocyanate derivatives, a trimer of isophorone diisocyanate containingan isocyanurate ring, etc. Among them, preferable ones are diisocyanatecompounds having isocyanate groups with different reactivity such as2,2,4-trimethylhexamethylene diisocyanate, tolylene diisocyanate, etc.

As the hydroxy group-containing ethylenically unsaturated monomer, it ispreferable to use an ethylenically unsaturated monomer having onehydroxyl group. Examples of such a monomer are hydroxyalkyl acrylatessuch as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,2-hydroxybutyl acrylate, etc.; hydroxyalkyl methacrylates such as2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate,2-hydroxybutyl methacrylate, etc.; N-methylolacrylamide,N-methylolmethacrylamide, etc.

It is preferable to react the polyvalent isocyanate with the hydroxygroup-containing ethylenically unsaturated monomer in amounts of 1.0/0.5to 1.0/0.7 in equivalent weight ratio in terms of isocyanate group ofthe former/hydroxyl group of the latter. Unreacted hydroxylgroup-containing ethylenically unsaturated monomer may be retained inthe reaction system. The reaction temperature is usually 0 to 150° C.,preferably 40 to 100° C. In the reaction, it is possible to use aurethane reaction catalyst such as dibutyl tin dilaulate, or the like.Further, it is possible to use a polymerization inhibitor such asbis(2-hydroxy-3-tert-butyl-5-phenyl)methane, hydroquinone, etc. Thereaction is preferably carried out in a suitable organic solvent. As thesolvent, there can be used methyl ethyl ketone, methyl isobutyl ketone,ethyl acetate, butyl acetate, Cellosolve acetate, etc.

The fluorine-containing resin used as the component (A) can also beproduced by reacting a hydroxyl group-containing fluorine-containingcopolymer with the above-mentioned isocyanate group-containingpolymerizable adduct. The polymerizable adduct can be obtained byreacting so as to have 0.001 to 0.025 mole of double bond per 100 g ofthe hydroxyl group-containing fluorine-containing copolymer. Thereaction is preferably carried out at a temperature of 20 to 150° C.,preferably 40 to 100° C., in an atmosphere or in a stream of an inertgas such as a nitrogen gas The reaction time is preferably from 30minutes to 5 hours. In the reaction, it is possible to use theabove-mentioned urethane reaction catalyst and polymerization inhibitor.The reaction is preferably carried out in the solvent mentioned above.

The fluorine-containing resin used as the component (A) can further beobtained by reacting a hydroxyl group-containing fluorine-containingcopolymer with an isocyanate group-containing ethylenically unsaturatedmonomer. The reaction can be carried out in the same manner a mentionedabove.

As the isocyanate group-containing ethylenically unsaturated monomer,there can be used isocyanoalkyl acrylates such as isocyanomethylacrylate, isocyanoethyl acrylate, isocyanobutyl acrylate, etc.;isocyanoalkyl methacrylates, such as isocyanomethyl methacrylate,isocyanoethyl methacrylate, isocyanobutyl methacrylate, etc.

The hydroxyl value (or number) of the hydroxyl group-containingfluorine-containing copolymer is usually 0.57 to 250, preferably 3 to120. When the hydroxyl number is too small, the introduction of doublebonds becomes insufficient. On the other hand, when the hydroxyl numberis more than 250, turbidity takes place when dissolved in a solvent toreadily lower water resistance of a coating film obtained therefrom. Thecopolymer preferably contains the fluorine in an amount of 1 to 60% byweight.

Examples of the fluorine-containing copolymer as those obtained bycopolymerizing a fluoroolefin, for example, a fluoroethylene such asmonofluoroethylene, difluoroethylene, chlorotrifluoroethylene,tetrafluoroethylene, 1,1-bis(trifluoromethyl)ethylene, or the like;hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinylether, hydroxypentyl vinyl ether, hydroxyhexyl vinyl ether and the likehydroxyalkyl vinyl ether wherein one or more hydrogen atoms in the alkylor vinyl group are replaced by one or more fluorine atoms; ethyl vinylether, propyl vinyl ether, butyl vinyl ether, hexyl vinyl ether or thelike alkyl vinyl ether wherein one or more hydrogen atoms in the alkylor vinyl group are replaced by one or more fluorine atoms; or cyclohexylvinyl ether or the like cycloalkyl vinyl ether wherein one or morehydrogen atoms in the alkyl or vinyl group are replaced by one or morefluorine atoms.

Examples of hydroxyalkyl vinyl ethers wherein one or more hydrogen atomsin the alkyl or vinyl group are replaced by one or more fluorine atomsare CF₂ ═CF-O-CH₂ OH, CF₂ ═CF-O-CF₂ -CH₂ OH, CF₂ ═CF-O-(CF₂)₂ -OH, etc.

The above-mentioned copolymer may contain as other copolymerizablecompounds ethylene, propylene, isobuytylene, vinyl chloride, vinylidenechloride, vinyl acetate, n-vinyl lactate, methyl methacrylate,ethylenically unsaturated monomers having at least one carboxyl groupsuch as unsaturated acids such as maleic acid, fumaric acid, acrylicacid, methacrylic acid, etc., carboxyalkyl vinyl ethers such ascarboxyethyl vinyl ether, carboxypropyl vinyl ether, etc., orfluorine-substituted compounds thereof, and carboxyalkyl oxyalkylvinylethers or fluorine-substituted compounds thereof.

In the above-mentioned copolymer, it is preferable to use thefluoroethylene so as to be contained in an amount of 40 to 60% by mole,and to use the hydroxyalkyl vinyl ether so as to make the hydroxylnumber 0.57 to 250, particularly preferably 3 to 120, and to make theacid number of the carboxyl group 0 to 20, particularly preferably 1.0to 10. When the content of fluoroethylene is too small, the improvementin weather resistance is insufficient, whereas when the content is toomuch, there bring about difficult problems in industrial production.When the hydroxyl number is less than 0.57, the introduction of doublebonds becomes insufficient, whereas when the hydroxyl number is over250, the solubility in an organic solvent is readily limited due to anincreased use amount of the hydroxyalkyl vinyl ether. From the viewpointof the solubility in the organic solvent, it is preferable to use thehydroxyalkyl vinyl ether in an amount of 15% by mole or less. On theother hand, when the acid number is more than 20, the solubility in theorganic solvent is readily limited.

It is preferable to use a cycloalkyl vinyl ether and an alkyl vinylether as a total in an amount of 5 to 60% by mole in thefluorine-containing copolymer used as the component (A). When the amountof the cycloalkyl vinyl ether and the alkyl vinyl ether is too small,the above-mentioned copolymer becomes difficult to be dissolved in anorganic solvent. On the other hand, when the amount is too much, theusing amount of the fluoroolefin or hydroxyalkyl vinyl ether undesirablydecreases. It is particularly preferable to use cyclohexyl vinyl etherand alkyl vinyl ether so as to make the content 5 to 45% by mole,respectively. It is preferable to use other components in amounts of 30%by mole or less.

As the component (B), there can be used at least one ethylenicallyunsaturated monomer copolymerizable with the double bonds of thecomponent (A). Examples of the component (B) are alkyl acrylates such asmethyl acrylate ethyl acrylate, butyl acrylate, isopropyl acrylate,2-ethylhexyl acrylate, etc.; alkyl methacrylates such as methylmethacrylate, ethyl methacrylate, butyl methacrylate, isopropylmethacrylate, 2-ethylhexyl methacrylate, etc.; styrene or styrenederivatives such as vinyltoluene, α-methylstyrene, chlorostyrene, etc.;acrylonitrile, methacrylonitrile, vinyl chloride, vinyl acetate, dialkylmaleates such as dimethyl maleate, etc. It is also possible to usepolymerizable monomer having one or more hydroxyl groups such ashydroxyalkyl acrylates, e.g., 2-hydroxyethyl acrylate, 2-hydroxypropylacrylate, 2-hydroxybutyl acrylate, etc.; hydroxyalkyl methacrylates,e.g., 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate,2-hydroxybutyl methacrylate, etc.; monoacrylates or monomethacrylates ofpolyhydric alcohols, e.g., glycerin, trimethylolpropane, etc.;N-methylolacrylamide, N-methylolmethacrylamide, or alkyletherifiedcompounds thereof, etc. If necessary, it is possible to use unsaturatedamides such as acrylamide, methacrylamide, etc.; polymerizable monomershaving an oxirane group such as glycidyl methacrylate, glycidylacrylate, etc.; α,β-unsaturated carboxylic acids and alkyl estersthereof such as acrylic acid, methacrylic acid, monoalkyl maleate, etc.

When the contents of the unsaturated amide and the polymerizable monomerhaving an oxirane group are too much, there is a tendency to lower waterresistance of coating film produced therefrom or the kind of reactionsolvent is limited. Thus, these monomers are preferably used in amountsof 30% by weight or less based on the total weight of the components (A)and (B). Further, when the content of the α,β-unsaturated carboxylicacid is too much, there is a tendency to lower water resistance of thecoating film. Therefore, it is preferable to use the α,β-unsaturatedcarboxylic acid in an amount of 10% by weight or less based on the totalweight of the components (A) and (B).

The graft copolymer can be obtained by polymerizing the component (A) inthe presence of the component (B) using the component (A) in an amountof 0.5 to 99.5% by weight and the component (B) in an amount of 99.5 to0.5% by weight. If the weight ratio of the components (A)/(B) is lessthan 0.5/99.5, the weather resistance and chemical resistance of thecoating film are lowered, whereas the ratio is more than 99.5/0.5,dispersibility of pigment, drying properties, compatibility with otherresins are lowered. It is preferable to use the components (A) and (B)in amounts of 10 to 90% by weight and 90 to 10% by weight, respectively.

The hydroxyl number of the graft copolymer can be adjusted bycontrolling the hydroxyl number of the component (A) and using amountthereof, and the using amount of the hydroxyl group-containingpolymerizable monomer used in the component (B). The acid value (ornumber) of the graft copolymer can be adjusted by controlling the acidnumber of the component (A) and the using amount of α,β-unsaturatedcarboxylic acid in the component (B).

The polymerization of the component (B) in the presence of the component(A) can be carried out, if desired, by using an organic solvent such astoluene, xylene, methyl isobutyl ketone, butyl acetate, ethyl acetate,Cellosolve acetate, butyl Cellosolve, 1-butanol, 2-butanol, 1-propanol,2-propanol, etc., as a reaction solvent, and a polymerization initiator.Examples of the polymerization initiator are peroxides such as benzoylperoxide, di-tert-butyl peroxide, cumen hydroperoxide, etc.; azobiscompounds such as azobisisobutyronitrile, etc. The polymerization can becarried out at 50 to 200° C. for 1 to 10 hours with heating. Thereaction is preferably carried out in an atmosphere or in a stream of aninert gas such as nitrogen gas. In order to make the amount of unreactedmonomer smaller, it is preferable to use both an azobis compound and aperoxide together.

The graft copolymer thus produced can be used as a lacquer compositionby dissolving it in an organic solvent, or as a curing type coatingcomposition by properly combining with a curing agent known as a curingagent for acrylic resin coating compositions. In the case of using thegraft copolymer as a coating composition as mentioned above, it ispossible to add inorganic pigments such as titanium white, cadmiumyellow, carbon black, etc., organic pigments such as phthalocyanineseries pigments, azo series pigments, etc., depending on purposes. Ifnecessary, the coating composition may contain one or more antioxidants,ultraviolet absorbers, photo stabilizers, pigment dispersants and thelike additives. These pigments are preferably used by well kneading withthe graft copolymer previously. The resulting coating composition issuitable for coating wood, metals, slates, roof tiles, etc.

As the organic solvent for use in the coating composition, those usedfor the graft polymerization can be used. The solid resin content in thecoating composition can be changed depending on purposes, and preferablyin the range of 20 to 50% by weight.

This invention is illustrated by way of the following Examples, in whichall parts and percents are by weight unless otherwise specified.

SYNTHESIS EXAMPLE 1

In a flask equipped with a thermometer, a stirrer, a nitrogenintroducing pipe and a reflux condenser, 210 parts of2,2,4-trimethylhexamethylene diisocyanate, 110.6 parts of methyl ethylketone, 0.166 part of dibutyl tin dilaulate, and 0.332 part ofbis(2-hydroxy-3-tert-butyl-5-ethylphenyl)methane [a polymerizationinhibitor] were placed and heated at 60° C. After adding 121.8 parts of2-hydroxyethyl acrylate dropwise uniformly over 1 hour, the reaction wascarried out at 60° C. for 2 hours to synthesize a polymerizable adducthaving an isocyanate group. The obtained solution had a solid content of70%. The content of the isocyanate group in the polymerizable adduct was9%.

SYNTHESIS EXAMPLES

In a flask equipped with a thermometer, a stirrer, and a refluxcondenser, 100 parts of xylene solution of a hydroxyl group-containingfluorine-containing copolymer [hydroxyl number 47; acid number 5;fluorine content about 27%, weight average molecular weight about 80,000(gel permeation analysis: converted to standard polystyrene), acopolymer containing trifluoroethylene and a hydroxyalkyl vinyl ether,the trifluoroethylene content about 50% by mole], the xylene solutionhaving a solid content of 50%, a specific gravity of 1.4 (g/cm³), aviscosity of about 800 cps (at room temperature) and using LUMIFLONLF-400 (a trade name, mfd. by Asahi Glass Co., Ltd.), 0.67 part of theisocyanate group-containing polymerizable adduct solution obtained inSynthesis Example 1 [0.47 part in terms of solid content], and 0.33 partof xylene were placed and reacted at 80° C. for 1 hour to yield afluorine-containing resin solution (solid content 50%) having reactivedouble bonds via a urethane linkage in an amount of 0.003 mole per 100 gof the resin. The resin solution had a hydroxyl number of 23.

SYNTHESIS EXAMPLE 3

A hydroxyl group-containing fluorine-containing copolymer (fluorinecontent about 41%, hydroxyl number 43, acid number 0, weight averagemolecular weight about 120,000 (gel permeation analysis, converted tostandard polystyrene), a copolymer of chlorotrifluoroethylene,hydroxyalkyl vinyl ether and fluorine atom-substituted hydroxyalkylvinyl ether) dissolved in a mixed solvent of butyl acetate, ethylacetate, methyl isobutyl ketone, toluene and xylene [solid content 50%,specific gravity 1.15 (g/cm³), a viscosity about 1000 cps (at roomtemperature)] in an amount of 100 parts, 0.67 parts of the isocyanategroup-containing polymerizable adduct solution obtained in SynthesisExample 1, and 0.16 part of xylene were reacted in the same manner asdescribed in Synthesis Example 2 to yield a fluorine-containing resinsolution (solid content 50%) having reactive double bonds via a urethanelinkage in an amount of 0.003 mole per 100 g of the resin. The resinsolution had a hydroxyl number of 21.

SYNTHESIS EXAMPLE 4

In a flask equipped with a thermometer, a stirrer and a refluxcondenser, 100 parts of xylene solution of the hydroxy group-containingfluorine-containing copolymer used in Synthesis Example 2, 0.3 part ofmaleic anhydride and 0.3 part of xylene were placed and reacted at 50°C. for 1 hour and at 100° C. for 2 hours to yield a fluorine-containingresin solution (solid content 50%) having reactive double bonds in anamount of 0.006 mole per 100 g of the resin. The resin solution had ahydroxyl number of 23 and an acid number of 4.

SYNTHESIS EXAMPLE 5

The hydroxyl group-containing fluorine-containing copolymer solution(solid content 50%) used in Synthesis Example 3 in an amount of 100parts, 0.3 part of maleic anhydride and 0.3 part of xylene were reactedin the same manner as described in Synthesis Example 4 to yield afluorine-containing resin solution (solid content 50%) having reactivedouble bonds in an amount of 0.006 mole per 100 g of the resin. Theresin solution had a hydroxyl number of 21 and an acid number of 1.5.

EXAMPLES 1 to 6, COMPARATIVE EXAMPLES 1 to 6

In a flask equipped with a thermometer, a stirrer, a nitrogenintroducing pipe and a reflux condenser, the ingredients listed inTables 1 and 2 were placed, respectively, and heated at 100° C. for 6hours with stirring in a nitrogen stream, followed by addition of 0.5part of benzoyl peroxide to further react at 110° C. for 2 hours withheating. To the resulting copolymer, xylene was added to adjust thesolid content properly. The obtained copolymer solutions had a solidcontent and an acid number as shown in Tables 1 and 2.

                                      TABLE 1                                     __________________________________________________________________________                      Example No.                                                                   1  2  3   4  5   6                                          __________________________________________________________________________    Ingredients                                                                         Resin solution                                                                            20*                                                                              50*                                                                              80* -- --  --                                               obtained in                                                                   Synthesis Example 2                                                           Resin solution                                                                            -- -- --  20*                                                                              50* 80*                                              obtained in                                                                   Synthesis Example 3                                                           Methyl methacrylate                                                                       20 12.5                                                                             5   20 12.5                                                                              5                                                Butyl methacrylate                                                                        60 37.5                                                                             15  60 37.5                                                                              15                                               Azobisisobutyro-                                                                          1.28                                                                             0.8                                                                              0.32                                                                              1.28                                                                             0.8 0.32                                             nitrile (initiator)                                                           Xylene      50 50 50  50 50  50                                         Properties                                                                          Solid content (%)                                                                         40.1                                                                             40.0                                                                             39.9                                                                              40.0                                                                             39.9                                                                              40.1                                             Acid number 0.5                                                                              1.3                                                                              2.0 0  0   0                                          __________________________________________________________________________     (Note) *in solid content                                                 

                                      TABLE 2                                     __________________________________________________________________________                      Comparative Example No.                                                       1  2  3   4  5   6                                          __________________________________________________________________________    Ingredients                                                                         Resin solution                                                                            20*                                                                              50*                                                                              80* -- --  --                                               obtained in                                                                   Synthesis Example 4                                                           Resin solution                                                                            -- -- --  20*                                                                              50* 80*                                              obtained in                                                                   Synthesis Example 5                                                           Methyl methacrylate                                                                       20 12.5                                                                             5   20 12.5                                                                              5                                                Butyl methacrilate                                                                        60 37.5                                                                             15  60 37.5                                                                              15                                               Azobisisobutyro-                                                                          1.28                                                                             0.8                                                                              0.32                                                                              1.28                                                                             0.8 0.32                                             nitrile (initiator)                                                           Xylene      50 50 50  50 50  50                                         Properties                                                                          Solid content (%)                                                                         40.0                                                                             39.9                                                                             40.1                                                                              39.9                                                                             40.0                                                                              40.1                                             Acid number 0.3                                                                              0.8                                                                              1.2 0.2                                                                              0.4 0.6                                        __________________________________________________________________________     (Note) *in solid content                                                 

The copolymer solutions obtained in Examples 1 to 6 and ComparativeExamples 1 to 6, a xylene solution (solid content 50%) of the hydroxylgroup-containing fluorine-containing copolymer used in Synthesis Example2 [Comparative Example 7], and a xylene solution (solid content 50%) ofthe hydroxyl group-containing fluorine-containing copolymer used inSynthesis Example 3 [Comparative Example 8] were subjected to thefollowing tests.

(1) Accelerated Weathering Test

(i) Each solution was adjusted with toluene to have a solid content of30% and coated on a bonderite #144 treated soft steel plate (mfd. byJapan Test Panel Co. Ltd.) with a bar coater so as to make the filmthickness 30 μm. After setting for 20 minutes, the coated film was driedat 80° C. for 20 minutes to give a test plate.

(ii) Using a Q-UV Accelerated Weathering Tester (mfd. by Q-Panel Co.,U.S.A.), the test plate thus prepared was exposed to cycling conditionsof UV irradiation at 50° C. for 4 hours - moisture condensation at 50°C. for 4 hours in each one cycle for predetermined time and the surfacegloss was measured on 60° gloss meter.

(2) Pigment Dispersibility Test

Each solution in an amount of 50 parts (as the solid content) was mixedwith 3 parts of carbon black and kneaded with a three-roll mill untilthe particle size measured by a grindometer became 10 μm or less. Then,the coating composition thus adjusted was allowed to stand at roomtemperature for 7 days to observe the separation (sedimentation).

(3) Resin Outer Appearance Test (i) Solution State

A graft copolymer solution was placed in a 300-ml glass-made beaker andthe state of the resin solution at 23° C. was observed by the naked eyeto measure transparency.

(ii) Film State

Each solution was flow coated on a glass plate, subjected to setting for20 minutes and dried at 108° C. for 3 hours. The state of resin film at23° C. was observed by the naked eye to measure transparency.

The results are as shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________                   Example No. Comparative Example No.                                           1 2 3 4 5 6 1 2 3 4 5 6 7 8                                    __________________________________________________________________________    Resin outer                                                                          Solution                                                                              Transparent Transparent                                        appearance                                                                           Film    Transparent Turbid      Trans-                                                                        parent                                 Accelerated                                                                          Initial gloss (%)                                                                     87                                                                              86                                                                              84                                                                              85                                                                              83                                                                              82                                                                              83                                                                              81                                                                              80                                                                              81                                                                              80                                                                              79                                                                              80                                                                              79                                   weathering                                                                           Gloss after                                                                           81                                                                              83                                                                              83                                                                              79                                                                              80                                                                              81                                                                              75                                                                              77                                                                              78                                                                              75                                                                              76                                                                              77                                                                              80                                                                              79                                          1000 hrs (%)                                                                  Gloss after                                                                           70                                                                              75                                                                              79                                                                              68                                                                              73                                                                              77                                                                              60                                                                              68                                                                              73                                                                              59                                                                              66                                                                              72                                                                              79                                                                              78                                          2000 hrs (%)                                                           Pigment                                                                              Separation                                                                            No separation                                                                             Slightly separated                                 dispersibility                                                                       (sedimentation)                                                               state                                                                  __________________________________________________________________________

The graft copolymer produced by the process of this invention can beused as a raw material for coating compositions, which can form acoating film with excellent weather resistance. The graft copolymer perse is excellent in transparency and pigment dispersibility.

What is claimed is:
 1. A process for producing a graft polymer useful asraw material of coating compositions having excellent transparency andpigment dispersibility which comprises polymerizing 99.5 to 0.5% byweight of an ethylenically unsaturated monomer (B) in the presence of0.5 to 99.5% by weight of a fluorine-containing resin (A) havingreactive double bonds via a urethane linkage, the amount of said doublebonds being 0.001 to 0.025 mole per 100 g of the resin (A) and saidfluorine-containing resin (A) being obtained by reacting afluorine-containing copolymer having hydroxyl groups derived from ahydroxyalkyl vinyl ether, an isocyanate compound having two or moreisocyanate groups and a hydroxyl group-containing ethylenicallyunsaturated monomer.
 2. A process according to claim 1, wherein thefluorine-containing copolymer having hydroxyl groups has a hydroxylnumber of 0.57 to 250 and a fluorine content of 1 to 60% by weight.
 3. Aprocess according to claim 1, wherein the ethylenically unsaturatedmonomer (B) is at least one member selected from the group consisting ofmethyl acrylate, ethyl acrylate, butyl acrylate, isopropyl acrylate,2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butylmethacrylate, isopropyl methacrylate, 2-ethylhexyl methacrylate,styrene, vinyltoluene, α-methylstyrene, chlorostyrene, acrylonitrile,methacrylonitrile, vinyl chloride, vinyl acetate, dimethyl maleate,2-hydroxyethyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxypropylacrylate, 2-hydroxypropyl methacrylate, monoacrylate of glycerin,monomethacrylate of glycerin, monoacrylate of trimethylolpropane,monomethacrylate of trimethylolpropane, N-methylolacrylamide, andN-methylolmethacrylamide.
 4. A process according to claim 1, wherein theethylenically unsaturated monomer (B) is methyl methacrylate.
 5. Aprocess according to claim 1 wherein the ethylenically unsaturatedmonomer (B) is at least one member selected from the group consisting ofan alkyl acrylate and an alkyl methacrylate.
 6. A process for producinga graft polymer which comprises a polymerizing 99.5 to 0.5% by weight ofan ethylenically unsaturated monomer (B) in the presence of 0.5 to 99.5%by weight of fluorine-containing resin (A) having reactive double bondsvia a rethane linkage, the amount of said double bonds being 0.001 to0.025 mole per 100 g of the resin (A) and said fluorine-containing resin(A) being obtained by reacting a fluorine-containing copolymer havinghydroxyl groups, an isocyanate compound having two or more isocyanategroups and a hydroxyl group-containing ethylenically unsaturatedmonomer, the fluorine-containing copolymer having a hydroxyl number of0.57 to 250 and a fluorine content of 1 to 60% by weight and being acopolymer containing as essential components a fluoro-olefin, a hydroxyalkyl vinyl ether and an alkyl vinyl ether or a cycloalkyl vinyl ether.7. A process according to claim 6, wherein in the fluorine-containingcopolymer having hydroxyl groups, the fluoro-olefin is contained in anamount of 40 to 60% by mole, the hydroxy alkyl vinyl ether is in anamount to provide the hydroxyl number of 0.57 to 250 and the cyclohexylvinyl ether or the alkyl vinyl ether is in an amount of 5 to 45% bymole, respectively.
 8. A process according to claim 6, wherein theethylenically unsaturated monomer (B) is at least one member selectedfrom the group consisting of methyl acrylate, ethyl acrylate, butylacrylate, isopropyl acrylate, 2-ethylhexyl acrylate, methylmethacrylate, ethyl methacrylate, butyl methacrylate, isopropylmethacrylate, 2-ethylhexyl methacrylate, styrene, vinyltoluene,α-methylstyrene, chlorostyrene, acrylonitrile, methacrylonitrile, vinylchloride, vinyl acetate, dimethyl maleate, 2-hydroxyethyl acrylate,2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxylpropylmethacrylate, monoacrylate of glycerin, monomethacrylate of glycerin,monoacrylate of trimethylolpropane, monomethacrylate oftrimethylolpropane, N-methylolacrylamide and N-methylolmethacrylamide.9. A process according to claim 6, wherein the ethylenically unsaturatedmonomer (B) is methyl methacrylate.
 10. A process according to claim 6,wherein the ethylenically unsaturated monomer (B) is at least one memberselected from the group consisting of an alkyl acrylate and an alkylmethacrylate.